In a plan released by his campaign, Walker also calls for requiring all unions to hold periodic votes so workers can decide whether they should continue to exist. If elected, he would also cancel President Barack Obama's Labor Day order that federal contractors provide paid sick leave and work to end policies requiring some salaried workers in the private sector to receive overtime — saying in some cases they should get time off instead.

"Our plan will eliminate the big government unions entirely and put the American people back in charge of their government. Federal employees should work for the taxpayers — not the other way around," Walker is to say in a town hall meeting at construction equipment maker Xtreme Manufacturing in Las Vegas.

Unions are braced for the speech and expected to react strongly against it.

"His whole theory of the case is fighting workers rather than helping working families," Randi Weingarten, president of the American Federation of Teachers, said before Walker unveiled his plan.

The far-reaching proposals are in keeping with what brought the Republican governor to national prominence and allowed him to mount a campaign for the presidency.

His plan — all but impossible to pass, according to one observer — goes further than what he's done in Wisconsin and would decimate private- and public-sector unions. That in turn would help Republicans at the ballot box because unions typically spend money to help Democrats.

Walker pitched his 2011 limits on collective bargaining as a way to solve the state's budget woes by forcing government workers to pay more for their benefits. But he likely would not see equivalent savings at the federal level because federal workers are already barred from negotiating over wages and benefits. Instead, they bargain over work schedules, workplace safety and the like.

Walker's move comes as his campaign is flagging. Viewed as a top-tier candidate for the first half of the year, Walker has seen his polling numbers plummet in recent weeks.